1. Field of the Invention
The embodiments described herein are directed to radio frequency communication systems, and more particular to systems and methods for extending the communication range in a radio frequency communication system.
2. Background of the Invention
Radio Frequency Identification (RFID) systems are a type of radio frequency communication system. RFID systems are gaining attention due to their ability to track and identify moving objects. In an RFID system, remote objects intended to be tracked and identified are equipped with a small RFID tag. The RFID tag contains a transponder and a digital memory chip that is given a unique electronic identification. An interrogator, or a reader can be configured to emit a signal that can activate the RFID tag. When an RFID tag passes within range of the reader, the RFID tag can detect the reader's signal and provide its identification information. The reader can be configured to decode the identification information, and in certain applications will write data to the RFID tag.
The signal generated by the reader is a Radio Frequency (RF) signal. RFID systems are generally configured to operate within four main frequency bands. The frequency bands are characterized by the frequency of operation for the RF signal generated by the reader. These bands include a low frequency band, i.e., 125 KHz or 134.2 KHz, a high frequency band, i.e., 13.56 MHz, a UHF frequency band, i.e., 868-956 MHz or 463 MHz, and a microwave frequency band, i.e., 2.4 GHz or 5.8 GHz.
An RFID reader generally comprises a radio transceiver configured to transmit and receive RF signal. The radio transceiver is coupled with one or more antennas that enable the transceiver to transmit and receive the RF signals. The transceiver is also interfaced with an encoder/decoder configured to decode information contained in the received signals and encode information to be transmitted via the transceiver.
RFID tags are generally classified as passive or active tags. A passive tag has no internal, or onboard power supply. Instead, a passive tag is powered by energy contained in the RF signal transmitted from the reader. The RF signal transmitted by the reader induces an electrical current in the tag antenna that supplies enough power to allow the tag to power up and transmit a response. Most passive tags signal to the reader by backscattering the RF carrier signal generated by the reader. This means that the tag antenna should be designed to both collect power from the incoming signal and also to transmit the outbound backscatter signal. It should be noted that the response signal generated by the tag can include more than just identification information.
An active tag, on the other hand, includes its own internal power source, which is used to power the tag in order to generate an outgoing signal. Active tags can have longer operational ranges and larger memories as compared to passive tags, which can allow the tag to store additional information sent by the reader; however, because passive tags do not require an onboard power supply, they can be made smaller and can cost significantly less than active tags. Additionally, due to their simplicity in design, passive tags are suitable for manufacture with conventional printing process for the antenna.
While passive tags provide many benefits that make them increasingly more popular for new RFID applications, one drawback is the limited operational range, e.g., as compared to active tags. One way to overcome the limited range problem, in certain applications, is to use a range extender. A range extender can be defined as an antenna, or resonator circuit, that can be placed between the reader and the tag and can be configured to receive the RF signal from the reader, amplify it, and rebroadcast it to the tag. Thus, the resonator circuit can be used to extend the range of communication ordinarily achievable between the reader and the tag.
Conventional range extenders do not necessarily help, however, when the limited range is due to some impediment to the RF signal being produced by the reader. RF signals are electromagnetic signals. Accordingly, the ability for a reader to communicate with the tag is dependent on the degree to which the RF signals produced by the reader and transmitted by the reader antenna magnetically coupled with the tag antenna. This means that the magnetic strength, or magnetic flux of the RF signal as seen by the tag is an important parameter.
Many materials act as magnetic flux blockers, i.e., they block the electromagnetic RF signals being generated by the reader. When limited communication range is the result of a magnetic flux blocker, a range extender will not necessarily overcome the problem. This is because the magnetic flux blocker will block the RF signals being generated and retransmitted by the range extender in the same manner that it will block the signals being generated by the reader.
As the applications for RFID technology grow, RFID tags are being included, or embedded in devices that are housed or contained in material that can act as a magnetic flux blocker. Accordingly, communication range can be limited for many of these new applications. Unfortunately, conventional range extenders will not necessarily be able to overcome some of the limited communication ranges for these new applications.